Table 1. Literature review of previous studies on the role of plant diversity in promoting or supressing herbivory.
Type refers to whether the species richness was manipulated (Experimental), natural species richness variation was taken advantage of (Observational), or the conclusion was based on estimates from previous literature (Meta-analysis). No study from the meta-analyses were repeated in this table. Consumer effect refers to whether the study estimated a measure of the amount of interaction between plants and consumers (Magnitude) – usually a damage measurement, or estimated the effect that interaction had on the plants’ fitness (Impact) – usually by measuring biomass in the presence or absence of herbivory. A positive relationship means that the study found that the magnitude or impact of herbivory increased with increasing plant diversity, a negative relationship means the study found that herbivory decreased with plant diversity. None means the study found no relationship between herbivory and plant diversity.
| Study | Type | Species richness range | Measured | Measured on effect | Consumer | Relationship |
|---|---|---|---|---|---|---|
| Lau et al. (2008) | Experimental | 1 vs. 16 | Leaf damage from generalists | 1 Legume sp | Magnitude | Positive |
| Mulder & Huss-Danell (2001) | Experimental | 1, 2, 4, 8, 12 | Leaf damage | Community | Magnitude | Positive |
| Plath et al. (2011) | Experimental | 1 vs. 3 | Leaf damage | 1 Rosea tree | Magnitude | Positive |
| Prieur-Richard, Lavorel & Linhart (2002) | Experimental | 3, 6, 18 | Leaf damage | 2 Conyza spp. | Magnitude | Positive |
| Scherber et al. (2006) | Experimental | 1, 2, 4, 8, 16, & 60 | Leaf damage | All species + 3 phytometer spp | Magnitude | Positive |
| Schuldt & Baruffol (2010) | Observational | 25–68 | Leaf damage | 10 tree spp | Magnitude | Positive |
| Vehviläinen, Koricheva & Ruohomäki (2007) | Meta-analysis | 1 vs. Several | Leaf damage | 2 tree spp (Oak & Alder) | Magnitude | Positive |
| Wang et al. (2010) | Observational | 1, 2, 4, 6, 8, 11 | #plants grazed by sheep | Community | Magnitude | Positive |
| Hanley (2004) | Experimental | 3, 6, 12 | Leaf damage by Mollusks | All spp | Magnitude | No |
| Sobek et al. (2009) | Observational | Natural range across German deciduous forest | Leaf damage by insects | 2 Maple spp | Magnitude | No |
| Yguel et al. (2011) | Observational | Natural range across managed French forest | Leaf damage | 1 Oak sp. | Magnitude | No |
| Jactel & Brockerhoff (2007) | Meta-analysis | 1 vs. Several | Leaf damage | Many individual spp. | Magnitude | Negative |
| Lau et al. (2008) | Experimental | 1 vs. 16 | Leaf damage from specialists | 1 Legume sp | Magnitude | Negative |
| Massey et al. (2006) | Experimental | 1 vs. 5 | Leaf damage | 1 Shorea sp | Magnitude | Negative |
| McNaughton (1985) | Observational | Natural range across Serengeti | % Biomass consumed | Community | Magnitude | Negative |
| Petermann et al. (2010) | Experimental | 1, 2, 3, 4, 6, 9 | Infestation by aphids | Community | Magnitude | Negative |
| Sobek et al. (2009) | Observational | Natural range across German deciduous forest | Leaf damage by insects | 1 Beech sp | Magnitude | Negative |
| Unsicker et al. (2006) | Observational | 18–45 | Leaf damage | Many individual spp. | Magnitude | Negative |
| Vehviläinen, Koricheva & Ruohomäki (2007) | Meta-analysis | 1 vs. Several | Leaf damage by insects | 1 Birch sp | Magnitude | Negative |
| Wilsey & Polley (2002) | Experimental | 1–4 (manipulated Evenness) | Infestation by spittlebugs | Solidago canadensis | Magnitude | Negative |
| Mulder & Huss-Danell (2001) | Experimental | 1, 2, 4, 8, 12 | Reduction of biomass in insecticide plots | Community | Impact | Positive |
| Scherber et al. (2010b) | Experimental | 1, 2, 4, 8, 16, 60 | % reduction of biomass in insect exclusions | Community | Impact | No |
| Hillebrand & Cardinale (2004) | Meta-analysis | 1–60 | Absolute and % reduction of bio-mass in grazer exclusion | Community of phytoplankton | Impact | Negative |
| Lanta (2007) | Experimental | 1, 2, 4, 6 | Reduction of biomass in Mollusk exclusions | Community | Impact | Negative |
| Narwani & Mazumder (2010) | Experimental | 1 vs. 4 | Biomass consumed | Community of phytoplankton | Impact | Negative |
| Pfisterer, Diemer & Schmid (2003) | Experimental | 1, 2, 4, 8, 32 | % reduction of biomass in insect exclusion | Community | Impact | Negative |
| Stein et al. (2010) | Observational | 15–37 | % reduction of biomass in insect exclusions | Community | Impact | Negative |